1. Field of the Invention
The present invention relates to battery powered industrial vehicles, such as lift trucks; and more particularly to monitoring the performance of the battery.
2. Description of the Related Art
Electric lift trucks employ large lead-acid batteries to power their traction and lift drives. Many lift trucks are operated almost continuously throughout three work shifts a day. When the battery becomes discharged, it is replaced and the truck is immediately put back into service. The battery that was removed is then recharged off the truck and prepared for use on another truck. In a warehouse serviced by many such trucks, batteries continuously cycle through stages including: recharging (typically 7 to 8 hours); cool down period (typically another 7 to 8 hours); and use (typically 7 to 8 hours). Therefore a typical warehouse many have 2 or 3 times the number of batteries as the number of industrial vehicles. Because is takes some time to replace these relatively large batteries, during which time the truck is out of service, an objective in this industry is to operate the truck as long as possible on a battery charge. To do this, however, one must accurately know the state-of-charge or present capacity of the battery.
It also is desirable to know when a particular battery is approaching the end of its useful life at which time it may no longer be recharged to a level sufficient for a reasonably long working period. Nevertheless it is undesirable from an economic perspective to take a battery out of service before absolutely necessary. In order to determine when a particular battery is approaching the end of its useful life operational data has to be gathered over days or weeks to be able to detect a performance degradation trend.
In addition, a need exists to be able to detect several operating conditions that indicate a need to perform maintenance or repairs on a battery. For example, repeated disconnection and connection of the battery to a truck and recharging equipment cause wear of the battery cable. That wear often results in power losses in the cable and thus inefficient battery use. Electric current leakage also can occur between the battery and the frame of the lift truck which may be disadvantageous.
Therefore, a need exists for a system and method that monitors performance of each battery for a fleet of lift trucks.